This invention relates to an improved caliper brake for use on bicycles and particularly for bicycles having wide tires, often referred to as mountain bicycles or off-the-road bicycles.
Mountain bicycles are capable of negotiating any terrain worthy of a road or footpath. They have "fat" or wide cross-section tires mounted on narrow rims; they also employ such features as wide-ratio derailleur gears, thumb shifters, BMX pedals, and heavy duty brakes, front and rear. Usually the handlebars are flat and the seat high and quickly adjustable.
These bicycles, being used off the road, necessarily encounter very adverse conditions that ordinary bicycles and even touring and racing bicycles would be unable to meet and survive. Rocks are hit; long expanses of mud are often encountered. Sharp turns, hills, valleys, narrow passageways, holes, ruts, dust, and mud are normal. The brake system is one of the major keys to success or failure.
It is noteworthy that in the very muddy 1983 NORBA National Championship Race almost all of the brakes--except the ones built according to the present invention--were either worn down or broken off by the end of the race, whereas those of the present invention were all still operative.
Many types of brakes that have been used successfully on narrow-tire bicycles, have proven unsatisfactory for use on wide-tire bicycles. Thus, although both drum and disk brakes provide some excellent characteristics, such as being resistant to wet conditions, they are too heavy, and the disk brakes are also quite expensive. They are complex and too easily damaged under severe off-the-road conditions. Moreover, since they transmit the braking torque through the spokes, they tend to loosen the spokes.
Cantilever brakes have heretofore been preferred for high quality bicycles of the wide-cross-section or balloon-tire type. Cantilever brakes are light, give good braking, and are inexpensive, but they have the disadvantage that they project out from the sides of the bicycle and as a result tend to catch on bushes or other obstructions and, consequently, be damaged and, in some cases, have resulted in injuries to the rider. Also, these brakes were originally designed for on-the-road or touring bicycles with narrow tires; therefore, although they generate enough pad pressure for good stopping at low to moderate speeds, even on bikes having wide tires, they are not powerful enough to take full advantage of the traction which wide-tire bicycles have, and at high speeds they tend to produce a fading and mushy effect. Similar problems are also traceable to the great traction of the wide tires and to the fact that they store much greater energy at high speeds.
The conventional sport bicycles with narrow tires have long used caliper brakes. However, when these conventional caliper brakes have been used on bicycles having the wide tires characteristic of mountain bicycles, both the center-pull and side-pull caliper brakes have tended to give an extremely mushy reaction, due to the lengthening of the brake arms in order to clear the wide-diameter tires, this lengthening resulting in excessive flexing. For that reason, caliper brakes have been looked down on by cyclists using off-the-road bicycles.
A problem found even when the better caliper type brakes are used on narrow-diameter tires, has been that they have not afforded independent adjustment of the return spring force on each side of the tire rim. Usually these caliper brakes have had only a single spring, which, of course, could not give the desired independent adjustment. However, even when the brake did employ two springs, those springs were not independently adjustable. As a result, it has been difficult to achieve the proper tension on the actuating cable, a tension which determines the return tension of the hand control lever. Yet, such adjustments are usually necessary because of the widely varying mechanical advantages among the different control levers being used, especially when they are applied to bicycles having wide-diameter tires.
For example, Magura motorcycle control levers have been used on many wide-tire bicycles in conjunction with upright motorcycle-type handlebars. The optimum cable-return tension necessary to return a Magura type of lever properly to its unactuated position is appreciably different from the tension necessary to return one of the levers likely to be used with the increasingly-popular drop bar used on wide-tire bicycles. These have distinctly different designs and have leverage ratios much different from those of the motorcycle-type levers. Since some riders prefer one type of lever and some prefer another, there will almost always have to be adjustments of the brake to the particular kind of lever being used.
There is also a problem with pad centering when the bicycle is used under the unusually adverse environmental conditions to which the mountain bicycles are subjected. Some prior-art bicycles have relied on a mounting bolt passing through the mounting plate. Others have used a combination of adjustable pad locations with the positioning effect of an actuating cable passing through a cable stop, as means for centering the pads; these are often called floating return spring systems. Such systems have been found to be unacceptable for use on wide-tire bicycles, because the centering is not positive enough to overcome the friction resulting from uneven mud buildups on the various parts of the brake. Since these bicycles are often used off the road, mud buildup is a common, and can be a very difficult problem, especially with this type of brake. Thus, although the pads may be perfectly centered before the ride begins, they become uncentered once heavy mud is encountered, and then one pad tends to rub on the rim while the other pad is distant from it.
The use of a mounting bolt passing through the mounting plate is more positive than the "floating return spring" systems, but even then the pad-centering systems requires a supporting member that is, in its own turn, mounted to the bicycle by one or more bolts. This increases the complexity, adds weight, and, if attempts are made to make it light, the resulting structure detracts substantially and effectively from the needed rigidity. Overall stiffness and rigidity of the brake system is necessary for this kind of bicycle because of the larger braking forces required, since there is much more tire traction from the wide-diameter tires. Also, the very fact that the tire profile is large means that the brake arms and mounting members must be longer if they are to clear the tire. If, when they are made longer, they are not rigid enough, they tend to squeal, due to high-frequency flex, and also tend to feel mushy to the rider. If they are made rigid, they add considerably to the weight.
Other problems relate to the cable clamp used to connect the cable to the brake. Some of the brakes pass the cable through a hollow bolt, and in this structure there is a tendency for the cable to become frayed or crimped so that service becomes difficult. In others, the cable is pulled through a slot in a curved plate, and this expedient appears also to result in fraying. Some brakes require an integral ferrule on the end of the cable; this is an undesirable approach because the brake-actuating levers used with these bicycles also have an integral ferrule, so that the cable core is trapped in the housing and cannot be removed for lubrication. Nor can the length be adjusted to accommodate the many different kinds of bicycles being used.
An additional problem is that of obtaining adjustment of the brake shoe--radially for radial alignment with the tire rim, rotationally along the axis of the brake caliper, and rotationally along the axis perpendicular to the caliper and to the plane of the tire. Also, inward adjustment toward the rim may be needed as the brake pad wears.
A further problem results from the fact that many bicyclists desire a quick-release system, enabling quick removing of a wheel and its tire from the bicycles. Quick removal saves a great deal of time, when tire repair must be made during as race, for example. Some brakes have them, but some do not, though it is considered by many users to be essential for wide-tire bicycles. Removal of narrow tires is not impeded by the brakes, for they are little wider than the rim. Heretofore, quick-release mechanisms have required additional apparatus, resulting in complexity or additional weight and adding to the number of things that can go wrong.
Thus, although many prior-art types of brakes are suitable for on-the-road bicycles, they are far from satisfactory for the stringent conditions under which mountain or off-the-road bicycles must operate and for use with the wide, large cross-section tires mounted on the narrow rims of such bicycles. Mountain bicycle brakes must meet all of the following requirements, and the prior-art brakes meet few, if any, of them:
(1) The brake must provide a powerful braking force and do this with high mechanical advantage in the brake structure, for the wide tires provide much more traction than do narrow tires, and braking force adequate for narrow tires is usually inadequate for wide tires.
(2) The brake arm must be rigid, whereas most prior-art brake arms tend to be flexible, especially when large braking forces and high mechanical advantages act on them. Longer arms give greater mechanical advantage, but their added length means that they are less rigid. This loss in rigidity counteracts the otherwise expected increase in braking effectiveness. Attempts to stiffen long arms add intolerable weight.
(3) The brake arms must be securely, strongly, and rigidly mounted to the frame. Securement by clamps results in looseness and brake mushiness, as well as susceptibility to damage under rough conditions, and in displacement that destroys braking effectiveness.
(4) The brake must have strong centering forces and high resistance to deflection forces, because of the rugged environment that imposes strong demands on the centering equipment. Poor centering results in friction and gross wear. Mud must be counteracted or got rid of.
(5) The brake needs strong spring tension as part of the centering force but also requires adjustability of each arm to obtain balance, and adjustments must be performed rapidly and with a standard tool, such as a light wrench that can be carried along. Different brake levers require different spring adjustments; different riders have different preferances; many riders feel that the tensions on the rear-wheel brake must be different from those on the front-wheel brake. Powerful jolts from chuck holes, rocks, etc. may require instant re-adjustment. Factory settings, therefore, are rarely satisfactory and are likely to remain satisfactory only for a short period of time.
(6) The brake must have a structure that renders damage unlikely. When a brake arm projects out beyond the frame, it is liable to be damaged quickly and severely and to become a safety hazard.
(7) The brake structure must be able to withstand the severe conditions imposed by the trails and open-country routes that mountain bicycles must endure, and also adverse weather conditions. The brake must be so placed, assembled, and structured that it will be able to endure mud without heavy accumulation or build-up thereof and to do so without being rendered inoperative or subjected to undue wear.
(8) the brake must be capable of quick release. The brake pads engage narrow rims, and the tires are wide. Narrow tires automatically enable easy release, but wide tires impede release from the brakes, and the brakes require special structure in order to enable quick release. It is usual in mountain bicycle races for the racer to have to make tire repairs, and time lost in taking off the wheel is significant. Prior-art brakes offer little help. Quick release is also useful for transporting the bicycle, for the wheel can be quickly removed so that the bicycle will fit into a car.
(9) Rapid and complete brake pad adjustment is needed. Many brakes are adjustable to some degree, but not in enough ways to solve the problems encountered by mountain bicycles.
(10) Asymmetric mounting of the brake pads, with most of the pad extending away from the frame and toward the direction of travel, is very desirable, especially for aiding in quick release, discussed in (8) above. Heretofore, asymmetric mounting has generally been in the reverse direction, which enabled mud buildup rather than reducing it.
(11) On the rear wheel brake, mounting at the bottom of the chain stays enables lessening of the mud problem, while mounting above the chain stays results in mud build-up. Chainstay mounting is also preferred because it is more rigid than seatstay mounting, for chainstays are shorter and thicker.
These eleven requirements call for a generally integrated solution. The brake parts should cooperate to achieve the needed results. An important object of the invention is to provide this integrated solution.
Among the other objects of the invention are the following: to provide an improved caliper brake for use on bicycles having wide tires; to provide for individual spring adjustment for each shoe of a caliper brake, while providing such spring adjustment in a way that resists misalignment; to provide braking force that increases dramatically in proportion to the deflection of the brake handles; to provide improved mounting of each caliper arm of a brake; to provide an improved quick release mechanism for a caliper brake; to protect the brake mechanism against damage or malfunction due to mud, water, and other exposures; to provide a brake mechanism that projects out a minimum amount, if any, from the bicycle frame; to provide an improved brake-pad mounting system enabling adjustment for most, if not all, adjustment needs; to provide for adaptability of the brake to a wide variety of bicycle types and sizes; to provide for an improved cable-to-cam attachment mechanism; and to provide for a rear brake capable of mounting on the frame portion parallel to the chain while avoiding mud buildup.
Other objects and advantages of the invention will appear from the following description of some preferred embodiments.